This invention relates to an internal combustion piston-cylinder apparatus where the movement of a free piston is used to create a vacuum in a cylinder and where outside air, gases, or vapors are subsequently allowed to enter the cylinder's vacuum through a device that produces work or energy from the flowing gases.
Free piston engines are well known and include single chambers with one piston, single chambers with multiple pistons, and pistons in separate chambers coupled together with rods or other mechanical devices. The majority of free piston internal combustion apparatuses are used to compress a gas. Another common use of free piston devices is to directly power an engine.
A very basic example of a free piston in one chamber is U.S. Pat. No. 727,067 (Blake and Bell, 1903). The free piston is propelled up a vertical cylinder in order to compress a gas. A more complex example of a free piston device with multiple chambers is illustrated in U.S. Pat. No. 1,571,615 (Babin, 1926). The purpose of this device is also to compress a gas. During a portion of this device's operating cycle the movement of the piston causes a partial vacuum in the cylinder. The vacuum is used to suck gas into the cylinder so that it can be compressed. These inventions represent early prototypes of free piston devices.
Hundreds of free piston devices using one or two pistons in a cylinder to compress a gas have been patented since 1900.
Four inventors between 1863 and 1876 experimented with a different type of free piston device. These devices all used a free piston to create a vacuum in a cylinder. The pressure difference between the atmosphere and the cylinder's vacuum was then used to pull a second piston into the cylinder's vacuum in order to power an engine.
British patent 2,098 (R. A. Brooman, 1863) shows a gas engine where the up stroke of a piston is performed by an explosion in a cylinder. The piston travels sufficiently far to create a vacuum in the cylinder. A second piston is subsequently pulled into the cylinder's vacuum by outside air pressure. The second piston has a piston rod attached to it. An elaborate mechanism is used to convert the up and down motion of the second piston into the rotary motion of an engine.
British patent 1,173 (F. W. Wenham, 1864) shows a gas engine consisting of two pistons in a cylinder with both ends open to the atmosphere. The first piston has a piston rod on it that is connected to a crank shaft. The second piston is driven by a gas explosion to the opposite end of the cylinder and travels sufficiently far to form a vacuum in the cylinder. The vacuum is secured by holding the second piston in place where it stops. The piston holding mechanism consists of driving two wedges driven against a flat rod connected to the second piston. The first piston is then sucked into the cylinder's vacuum, turning a crack shaft for an engine. In this device mechanisms are also needed to translate the up and down motion of the piston into the rotary motion needed for an engine.
U.S. Pat. No. 168,623 (Daimler, 1875) describes an apparatus where a fuel/air mixture is ignited in a cylinder to propel a free piston to the point where the expansion and cooling of combustion products create a partial vacuum in the cylinder. The free piston is fitted with loose conical rings connected to springs that allow the piston to become wedged into a conical section at the upper end of the cylinder. By using this piston holding mechanism, a vacuum is secured in the cylinder. A second loose piston with a piston rod attached to it is then pulled into the cylinder's vacuum in order to power an engine.
In U.S. Pat. No. 178,023 (Otto, 1876) a free piston is driven to one end of a cylinder by an explosion so that the products of the explosion cool and condense and create a partial vacuum in the cylinder. A second piston is then forced into the cylinder by the atmospheric pressure. The second piston is connected to cranks on a fly wheel shaft.
The free piston devices of Wenham, Brooman, Daimler, and Otto all use the vacuum created in a cylinder to pull a piston with a rod connected to it into a cylinder. None of these apparatuses utilizes the vacuum that is created in the cylinder as a basis for a vacuum pump, evaporator, or gas evacuation device. None of the apparatuses allows air, gas, or vapors from outside the cylinder to enter the cylinder's vacuum in order to produce work or energy from the gases flowing into the cylinder's vacuum. All of these inventions needed cumbersome mechanisms to translate the pistons up and down motion into rotary motion. Because of the drawbacks inherent in these mechanisms, there is little evidence that these or other inventors pursued the concept of creating a vacuum in a cylinder to drive an engine after 1876.
In addition to the above patents, there are a few other examples where a free piston is stopped and held in place after a combustion gas expansion. In U.S. Pat. No. 4,491,095 (Feinberg, 1995) a free piston engine includes a mechanism to restrain a piston and hold in place as part of an engine cycle. This mechanism that grabs hold of the piston when its velocity goes to zero. The piston holding mechanism is a three jawed collet supported by needle bearings on tapered ways. This mechanism is released by a solenoid having a short stroke with a high force. The purpose of the holding mechanism is to provide a variable dwell between each cycle. The purpose of holding the piston is not to create a vacuum in a cylinder.
In U.S. Pat. No. 5,144,917 (Hammett, 1992) a free piston is restrained during an engine cycle. Hooked detents are situated at each end of the cylinder to catch and hold the piston in a fixed position during a portion of the combustion cycle. The purpose of this device, however, is to compress gas, not to create a vacuum in a cylinder.
U.S. Pat. No. 4,399,368 (Bucknam, 1983) depicts an apparatus that restrains a free piston after a gas expansion cycle in order to create a partial vacuum in a cylinder. Liquid at the bottom of a cylinder is heated using a solar beam to vaporize the liquid. The vapor pushes a piston up a vertical cylinder. The piston is held in place and the vapor is allowed to condense and form a vacuum below the piston. The piston is then released and pulled into the cylinder's vacuum to generate an electric current. This device, however, does not use an internal combustion process. Its does not allow air, gas, or vapors to flow into the cylinder as a means to produce work or energy.
One of the most common devices to create a vacuum for industrial evaporators or gas evacuation equipment is a steam jet ejector. Steam jet ejectors have few moving parts, but their energy efficiency is very low. Steam jet ejectors use high pressure steam rather than an internal combustion process to create a vacuum.